Photolithography techniques include processes in which, for example, a resist film composed of a resist composition is formed on top of a substrate, the resist film is selectively irradiated with light or an electron beam or the like, through a photomask in which a predetermined pattern has been formed, and a developing treatment is then conducted, thereby forming a resist pattern of the prescribed shape in the resist film. Resist compositions in which the exposed portions change to become soluble in the developing liquid are termed positive compositions, whereas resist compositions in which the exposed portions change to become insoluble in the developing liquid are termed negative compositions.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of miniaturization. These miniaturization techniques generally involve shortening the wavelength of the exposure light. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) have been introduced, and ArF excimer lasers (193 nm) are now also starting to be introduced. Further, investigations are also being conducted into the use of even shorter wavelengths such as F2 excimer lasers (157 nm), extreme ultra violet radiation (EUV), electron beams, and X-rays and the like.
Furthermore, in order to reproduce patterns of very fine dimensions, resist materials with high resolution are required. Chemically amplified resist compositions, which contain a base resin and an acid generator that generates acid upon exposure, are used as these types of resist materials.
For example, a positive chemically amplified resist includes a resin component that exhibits increased alkali solubility under the action of acid and an acid generator component that generates acid upon exposure, and during resist pattern formation, when acid is generated from the acid generator as a result of exposure, the exposed portions become alkali-soluble.
As the resin component of the chemically amplified positive resist composition, a polyhydroxysyene (PHS) based resin in which the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups, or a resin having structural units derived from (meth)acrylic acid within the principal chain (namely, an acrylic-based resin) in which the carboxyl groups have been protected with acid dissociable, dissolution inhibiting groups is generally used.
Examples of the acid dissociable, dissolution inhibiting groups include so-called acetal groups, such as chain-like ether groups typified by 1-ethoxyethyl groups, and cyclic ether groups typified by tetrahydropyranyl groups; tertiary alkyl groups typified by tert-butyl groups; and tertiary alkoxycarbonyl groups typified by tert-butoxycarbonyl groups (for example) see patent document 1).
During the production of semiconductor elements and the like, the resist films formed using resist compositions are usually thin films having a film thickness of approximately 100 to 800 nm, although resist compositions are also used for forming films of greater thickness, for example, in the formation of thick-film resists having film thicknesses of 1 μm or greater.
For example, when mounting LSI (Large Scale Integration) within electronic machinery, a thick-film resist is used in a multi-pin thin-film mounting process used for providing connection terminals composed of protruding electrodes on the upper surface of a support such as a substrate, wherein the thick-film resist is used for forming connection terminals composed of bumps that protrude from the support, or for forming connection terminals formed from a support pillar known as a metal post that protrudes from the support, and a solder ball that is formed on top of the metal post. In a specific example, these connection terminals can be formed by forming a thick-film resist on top of a support, exposing the resist through a predetermined mask pattern and then developing the resist to form a resist pattern in which the portions in which the bumps or metal posts are to be formed have been removed (stripped), filling these removed portions (resist-free portions) with a plating of a conductor such as copper, gold, nickel or solder, and then removing the surrounding resist pattern.
Examples of known resist compositions used for applications such as the formation of the above thick-film resists include positive photosensitive resin compositions containing a quinonediazide group-containing compound, which are used for forming bumps or wiring (for example, see patent document 2).
Resist patterns formed in the manner described above can be used for plating processes in which the resist pattern is used as a frame, and also for etching processes and high-energy implantation processes and the like in which the resist pattern is used as a mask. Accordingly, the resist patterns can be used in the production of MEMS (Micro Electro Mechanical Systems) in which the types of processes described above are performed.
MEMS are highly advanced micro systems in which micromachining techniques are used to integrate a variety of microstructures (including functional elements such as sensors, and conducting structures such as wiring and connection terminals) on top of a support. For example, patent document 3 discloses a method of producing a micro-device such as a magnetic head using a resist pattern of a specific shape formed using a positive resist composition containing a novolak resin.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2002-341538    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2002-258479    [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2002-110536